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- 1. Molecular Composition of Gases <ul><li>Objectives </li></ul><ul><ul><li>State Avogadro’s Law and explain its importance </li></ul></ul><ul><ul><li>Solve problems using the ideal gas law </li></ul></ul>
- 2. Avogadro’s Law <ul><li>So far, we have studied three gas laws: </li></ul><ul><ul><li>Boyle’s </li></ul></ul><ul><ul><li>Charles’ </li></ul></ul><ul><ul><li>Gay-Lussac’s </li></ul></ul><ul><li>A fourth law, called Avogadro’s Law , gives us a relationship between the volume of a gas and the number of moles of that gas (at the same temp and pressure) </li></ul>
- 3. Avogadro’s Law <ul><li>naturally, this law has a formula: </li></ul><ul><ul><li>V = kn </li></ul></ul><ul><ul><li>where V= volume </li></ul></ul><ul><ul><li>k = the proportionality constant (same for all gases) </li></ul></ul><ul><ul><li>n = number of moles of gas </li></ul></ul><ul><li>In plain English, it states "Equal volumes of ideal or perfect gases, at the same temperature and pressure, contain the same number of molecules." </li></ul>
- 4. Avogadro’s Law and its Significance <ul><li>Avogadro’s Law isn’t so much used to calculate as it is used to explain the relationship between the volume of any gas at STP. </li></ul><ul><li>It has been determined that 22.41 L of argon at 0°C and 1 atm has a mass of 39.95 g </li></ul><ul><li>Therefore, 22.41 L is the volume of 1 mole of any gas at STP. </li></ul>
- 5. The Ideal Gas Law <ul><li>No gas perfectly follows all four gas laws under all conditions. However, the assumption that they do holds true for most gases and in most conditions </li></ul><ul><li>To study gases and their behavior then, is to assume that the gas is an “ideal” gas and follows all four gas laws (Boyle’s, Charles’, Gay-Lussac’s, & Avogadro’s) </li></ul>
- 6. Ideal Gases <ul><li>do not condense into a liquid at low temperatures </li></ul><ul><li>do not have an attractive or repulsive force between particles </li></ul><ul><li>is composed of particles that have no volume </li></ul>
- 7. Ideal Gas Law <ul><li>On those assumptions, we can combine the gas laws into one equation that gives us the relationship between all four variables: </li></ul><ul><ul><li>pressure </li></ul></ul><ul><ul><li>temperature </li></ul></ul><ul><ul><li>volume </li></ul></ul><ul><ul><li>number of moles </li></ul></ul><ul><ul><li>PV = nRT </li></ul></ul>
- 8. Ideal Gas Law <ul><li>PV = nRT </li></ul><ul><li>P = pressure </li></ul><ul><li>V = volume </li></ul><ul><li>n = number of moles </li></ul><ul><li>R = proportionality constant </li></ul><ul><li>T = temperature </li></ul>
- 9. The Proportionality Constant <ul><li>If units of kilopascals and Liters are used, the value of R is: </li></ul><ul><li>8.314 L kPa ---------------------- mol K </li></ul>
- 10. The Proportionality Constant <ul><li>If pressure is given in atm (instead of kPa): </li></ul><ul><li>0.0821 L atm ---------------------- mol K </li></ul>
- 11. Ideal Gas Law <ul><li>this relationship and formula describes the behavior of gases very well at room temperature and atmospheric pressure </li></ul><ul><li>as the volume of the gas decreases , however, the attraction of the particles make the volume less than the formula would predict </li></ul><ul><li>at extremely high pressures , the volume of the particles themselves is close to the total volume so the formula will predict a lower volume than what actually exists </li></ul>
- 12. Deviation of Real Gases from Ideal Behavior
- 13. Practice Using Ideal Gas Law <ul><li>pg 435 # 1 - 4 </li></ul>

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